1. Field Application of the Invention
This invention relates to a technique for detecting, at high speed, as to whether a plurality of points specified on a pattern of detected binary picture image are properly connected through the pattern. The invention is further concerned with a method and apparatus for detecting the presence of pattern defects and, more specifically for detecting the electric conduction of a printed circuit pattern without contact and at high speed.
2. Description of the Prior Art
When inspecting a circuit pattern for defects, the circuit pattern is detected by a linear sensor or the like in order to obtain a binary picture image for detecting defects such as disconnection, short circuit and others, and to determine whether the specific points are concatenated through a pattern on the detected picture image. Arts disclosed in Japanese Patent Publication No. 16217/1983 "DETECTING METHOD FOR CONCATENATED DOMAINS" and "A STUDY OF RUBBING OUT AND NUMBERING CONCATENATED DOMAINS" (Shingaku Giho, the Journal of the Institute of Electronics and Communication Engineers of Japan, IE78-9) will be taken up for method to check a concatenation of such binary picture image pattern. However, the techniques disclosed above are intended for separating and extracting each of concatenated elements of the patterns (portion with the value 1 or 0) of the detected binary picture image.
Consequently, when five independent patterns (each being a closed domain pattern with binary logic level 1 as shown, for example, in FIG. 31 are present in the form of binary picture image, numbers 1 to 5 called labels, are given to all the patterns, as indicated from processing on the above-mentioned methods, and these labels are stored into a memory in a table format. The word "label" as used above is representative of a pad number or a temporary number subsequently given. However, such separation of all the patterns is not always required in order to be able to inspect defects such as a disconnections and others, and only a concatenation namely, a connectivity among the three points with a mark x thereon should be detected. In such cases, the labels 1, 4 and 5 are not required.
When an object pattern to be checked for defects, as a whole, is very complicated, a conceivable method is such that continuity will be detected concurrently while detecting the binary picture image line by line, horizontally, for example, by means of a linear sensor. In this case, for example, if the concatenation, or the connectivity, is checked by detecting the binary-coded picture image sequentially on a horizontal detection line from above as shown in FIG. 32, patterns with labels 1, 2 put thereon are judged to be separate at a point in time coming as late as a detection line l1. However, it is found that the patterns with labels 1, 2 are connected according to the detection line l2 appearing subsequently, which must be stored in a table on the memory. FIG. 33 indicates a construction of the table, wherein addresses 1, 2 (relative addresses in practice) are assigned the corresponding labels 1, 2, respectively, and as a data of the content, the labels 1 and 2 are written as they are when patterns with the labels 1, 2 are decided to be still isolated. However, when these are found to be continuous, the data are rewritten to the smaller value. FIG. 33 indicates the state after correspond to a representative value, for example, data have been rewritten, and thus it is found that the patterns with the labels 1, 2 are of the same type and are connected consequently. Further, if the patterns given in FIG. 32 are branched into n branches upward, n units of addresses and n units of data coordinated therewith are stored in the data table of FIG. 33.
As described above, when a connectivity of all the patterns is extracted during detection of the binary picture image on a linear sensor or the like according to the prior art, the memory capacity must be large enough to store or load labels equal in number to the connected patterns present on the binary picture image of FIG. 31 and extra labels (n-1 pieces of extra labels) become necessary in the case of a pattern branched plurally upward, as in the FIG. 32. However, in case where the pattern to be detected is not simple like FIG. 31 but FIG. 32 and is a circuit pattern, or the like, which is excessively complicated and large, the prior art technique would add the requirement that the working memory capacity be exceedingly large. Consequently, processing requires an enormously long time therefor, so that a real connectivity is difficult to be extracted.
There is a pattern inspecting art applicable to that for extracting the pattern connectivity. That is, a pickup system and a processing system for expanding and contracting the binary picture image are combined with the connectivity extracting art. As an associated art with such pattern inspecting art, which was disclosed in Japanese Patent Laid-Open No. 179343/1983, will be taken up.
The technique calls for detecting the number of detected binary patterns or the contracted patterns or the expanded patterns thereof within a specific range, comparing them with the number of patterns obtained from a standard pattern, and judging them to be defective when both numbers do not coincide. Thus a strict pattern alignment at each detected picture image is not required.
However, the conventional art cannot accurately indicate the position of a defect. Further, when a pattern separation (disconnection) or a pattern fusion (short circuit) simultaneously occurs within the specific range for counting the respective number of patterns, the number of patterns does not vary from the standard number of patterns; consequently, defects may be overlooked.